Agreed, but no one has stated she'd dead either. And Nika did see her once more after the event at the cabin, which was also mentioned in the session with Amber (which is not proof either way). The stuff with Emilio occurs to Nika before (he thinks to himself ...all sorts of information), in the car right after he and Bella leave, and before going to dinner at Nick's. 'I have to see this Emilio. Bella said he could get information... Maybe he can give me some peace of mind.' So it's definitely a tangent Ocean's pushing, which is why Emilio's presence in WiaB makes so many things possible. The one I first mentioned is if you tell Vic about what happened with the eraser, I'm guessing you have to be on her path - it happens after you kiss her while the others are out of the room.
It could be Nika flipped out and is in subconscious denial, but so far we've got two people who know something about Summer, Nia, and Elsa. Elsa posts a moody social media post, days later, so she was affected by having the past brought back, and Nia never saw her again. So all we know is it's serious, Nika has no closure and Nika thinks she's missing. Noji also says "These thoughts you have... Summer's disappearance... it all affected you too much."
If Summer was dead, Nami's damn insensitive when she confronts Nika at the hospital - "we were all shocked when the Summer thing went down, but man, it's been years, get over it!"
So currently, the indications are that SUmmer disappeared in someway rather than died, or everyoen is masking it to keep Nika from flipping out. THe question is also what happened to Summer's parents? Presumably they were out west as well? Summer was Nia's friend and Nia went to Tropics out west, where she knew Nami and Nika. I guess we have to wait for more info to be drip fed to us.
Regarding why no one else has, well, maybe not enough people have friends with connections like Emilio? Or, something random happened and her parents died, with the case unsolved. People can stay missing for a while if they choose, there was that British kid who was just found in France, having lived off grid for over 5 years in the news not so long ago. BUt for it to be shocking, there's some kind of foul play. I guess keep in mind there were corrupt police in Wollust in the original WiaB, Leia wants to corrupt more police and Cerill doesn't look so wholesome. Corrupt police coverups wouldn't be implausible given WiaB's set up.
